The invention to a fluid-bed reactor for biological effluent treatment with carrier particles for biocatalysts, having a system for separating out the carriers in the effluent outflow and a device for recycling the solids particles in the reactor tank.
In effluent treatment, carrier bodies for the microorganisms are increasingly used in order to increase the activity. Both fixed-bed reactors and fluid-bed reactors are used in this process. In fixed-bed reactors, only a part of the reactor space is utilised because of irregular growth which establishes itself naturally. Moreover, uniform process conditions (such as, for example, pH value) cannot be maintained in the fixed bed. In the event of fluctuations of the concentration in the feed, the buffering action of submerged biology is not fully exploited due to inadequate mixing.
Thoroughly mixed fluid-bed reactors, in which the carriers for the microorganisms are suspended are therefore more suitable for effluent treatment. The German patent specification No. DE-A 3,829,873, describes how the fluidisation mixing is effected by supplying gas to the liquid.
In longitudinal-flow units with a large length/width or height ratio, the solids particles are, in spite of relatively ideal mixing of the liquid phase, transported to the reactor outlet and concentrated there in the vicinity of the retention device, with the result that the major part of the reactor remains free of particles. Since a large part of the microorganisms is located on the solids particles, only restricted biodegradation of the effluent load takes place with this procedure. It is therefore necessary to ensure, by special measures, that the particles are distributed relatively uniformly throughout the reactor contents. Hitherto, special gas supply techniques, (see, for example, European Patent No. 0,163,159) or mechanical recycling (German Patent No. 3,408,759) have been proposed for solving this problem.
In the gas supply technique, a simultaneous reduction of the gas supply intensity in the longitudinal direction of the effluent tank is accepted. Since, however, the gas supply intensity must not be less than that required for fluidizing the solids particles, this technique can be applied only with increased energy consumption.
In mechanical recycling, the particles are removed from the tank by an airlift and transported by a conveyor belt to the inlet of the effluent tank. The disadvantage in this method is the additional expense on investment and energy costs.